The bactericidal properties of divalent silver for water treatment is the subject of U.S. Pat. No. 5,017,285 of the present inventor. In said patent the inventor has claimed a method for controlling the growth of bacteria in swimming pool and industrial cooling tower waters utilizing soluble divalent silver complexes with inorganic ligands which exhibit distinct advantages over monovalent silver in terms of cost, efficacy, concentration and stability. It was found that water sources having sodium chloride present at concentrations as high as 100 PPM would not precipitate insoluble chloride in contradistinction to monovalent silver at the same concentration of parts per million of available silver. While said divalent silver compounds are effective in brackish waters and swimming pools having these concentrations of salt, a major problem arises under conditions of higher salt concentrations and in special situations where higher halide concentrations are likely to prevail.
The situations where higher halide concentrations are likely to occur are manifold. Among the more prevalent cases are when sea water is used in swimming pools, which is a common occurrence at sea resorts, when brackish water is employed in cooling towers, and when swimming pools are maintained with calcium chloride in order to mineralize them. Another case is hot tubs with mineral salts.
When the aforementioned divalent silver compounds are added to said high halide concentration waters, a white curdy precipitate occurs which clouds the water to which it is added and makes it aesthetically unacceptable, even though the divalent silver performs its bactericidal action under these conditions of use. Accordingly, it was desirable to explore and test divalent silver compounds which would not produce a curdy halide precipitate in water containing high concentrations of salt or other halide salts.
Another problem associated with the divalent silver solutions is that care must be taken that they not contact the skin as they leave unsightly and difficult to remove silver stains. Although this problem was ancillary to the halide curdy precipitation problem, it was preferable that the divalent silver compound selected be more amenable to customer handling and remove the risk of, or minimize, silver staining.